Project Summary/Abstract Autoimmune Addison?s Disease (AAD) is a life-threatening endocrine disorder caused by the immune- mediated destruction of the adrenal cortex. Affected individuals lack key hormones that are critical for normal homeostasis. Because of this, patients with AAD are at high risk of developing a potentially deadly adrenal crisis characterized by hypotensive shock, vomiting, and life-threatening electrolyte abnormalities. Limited progress has been made over the past half-century in developing new therapies for AAD, in part because there is no actively studied animal model for the disease. Fortunately, dogs provide an opportunity for this very purpose. The disease is naturally occurring in both humans and dogs, and shares similar clinical, genetic, and immunologic underpinnings in both species. The goal of this study is to lay the groundwork for a canine model system to study AAD by characterizing the antigen-specific T cells that trigger the disease and determining the peptide sequences recognized by these T cells. Specifically, we will test the hypothesis that AAD is triggered by IFN-g- producing CD4+ T cells that are activated by peptides derived from steroid-producing enzymes in the adrenal cortex. Once we have identified and characterized these key players involved in triggering the immune system dysfunction in AAD, we can begin to develop approaches that manipulate or downregulate the aberrant immune response. Ultimately, we expect to use this canine model system to drive advances in our understanding of AAD and to foster the development of novel immunotherapies for humans. The work proposed in this application will be conducted at the renowned Center for Immunology at the University of Minnesota, and will provide a critical training opportunity in T cell biology, autoimmune disorders, and the benchtop methods required to study these topics comprehensively.